GCM projections for the Pacific Decadal Oscillation under greenhouse forcing for the early 21st century

Abstract The climatology and hydrology of western North America display strong periodic cycles which are correlated with the low‐frequency Pacific Decadal Oscillation (PDO). The PDO's signature is seen throughout the entire North Pacific region, with related significant associations to hydrology and ecology in western North America and northeastern Asia. Therefore, the status of the PDO in a warmer world caused by anthropogenic climate change is of great interest. We developed early 21st‐century projections of the PDO, using data from archived runs of the most recent high‐resolution global climate models from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (Phase 3 of the Coupled Model Intercomparison Project). Because of the geographical adjacency and hypothesized interactions between the PDO and the El Niño‐Southern Oscillation (ENSO), and between the PDO and the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), we also developed concurrent projections of ENSO and the NAO and examined their relationships with the projected PDO. For the B1, A1B and A2 Special Report on Emissions Scenarios (SRES) emission scenarios, the PDO projections for 2000–2050 showed a weak multi‐model mean shift towards more occurrences of the negative phase PDO, which becomes statistically significant for the time period 2000–2099. However, not all the models showed a consistent shift to negative PDO conditions. Copyright © 2011 Royal Meteorological Society